You create your own Where's Waldo game
You create your own Where's Waldo game on a piece of paper. You want your friend to find Waldo but they think you might be pulling a prank on them by not putting Waldo on the paper at all.
How can you prove to your friend that Waldo is on the paper without ruining it for them?
Cut a small hole in a piece of paper that is just large enough to see Waldo. This way you don't reveal anything about where he is, just that he is there.